Method and apparatus for making air insulated cable



May 27, 1947. H. D. ISENBERG METHOD AND APPARATUS FOR MAKING AIR INISULATED, CABLE Filed Feb. 3, 1945 HIGH FREQUENCY DRIVE MECHANISM FIG. 3

IN V EN TOR.

HANS D. 1%5N B ERG M ffl/m/ ATTORNEYS @atented May 27, 1%?

idbit? surge earner t diilwd METHOD awn WPARATUS EUR am HNSULATW CMQLE Hans D, Hsenherg, Wilmette, Ill.

Application February 3, 1945, Serial No. 576,0?9 in Claima (or. sz-e) tionally comprised of two coaxially arranged conductors which are held apart by insulating discs provided at spaced points along the two conductors to support the inner conductor centrally within the outer conductor and thus provide a dielectric air space therebetween. Manual methods are usually employed in assembling the discs upon the inner conductor and within the outer conductor. This is not only costly, but requires that the cable be formed in relatively short lengths or sections which must be Joined in order to obtain a cable of anyconsiderable length.

. It is an objectof the present invention, therefore, to provide improved methods and apparatus for continuously forming an air insulated or coaxial cable of any desired length.

It is another object of the invention to provide an improved method for the purpose described,

which requires a minimum of manual labor in the practice thereof and may be utilized to produce completed cable at a high production rate.

It is a further object of the invention to provide improved and exceedingly simple apparatus which is positive and reliable in its operation to produce air-insulated cable continuously and at a high production rate.

It is still another and more specific object of the invention to provide improved methods and apparatus for forming around a continuously moving conductor an insulating supporting structure upon which an outer conductor or covering may be wrapped to provide an air insulated cable.-

The invention, both as to its organization and method of operation, together with further obiects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which: i

Fig. l is a view schematically illustrating improved apparatus for continuously making air insulated cable, which is characterized by the features-of the present invention;

Fig. 2 is a side view partially in section, illustrating a segment of the cable produced by use of the apparatus shown in Fig. 1; and

iii

Fig. 3 is an end sectional view taken along the lines 3-3 in Fig. 2*.

Referring now to the drawings and more parductor i2 is fed, to so var the diameter of the helical convolutions' it that certain thereof, 1. e., the convolutions Eda are radially spaced from the conductor to support the outer sheath 2i, and others thereof, i. e., the convolutlons lib, engage the conductor I? at spaced points along the length thereof to support the radially spaced convolutions ltd from the conductor.

More specifically considered, the convolution forming mandrel 20 is slidably supported within the sleeve portion the of a. fixed support 3! and is provided with a tapered central bore 2! through which the inner conductor 82 is fed from a supply spool l8 over a. rotatably supported guide roll l9. This mandrel also extends within the sleeve portion 30a of a rotatable feeding element or table 30 which is supported upon the upper surface of the supporting member 3| by means of ball bearings 32. Adjacent the periphery thereof, the feed tabletli carries an angularly disposed post 29 upon which'a supply spool 28 for the filamentary element ii of insulating material ,is rotatably supported' The element Ii is carried through a feed eye 802) provided at the end of an arm 300 which is anchored to the sleeve portion 300. of the feed table 30. Thus the entire filament feed assembly comprising the rotatable table 30 and this mandrel is provided at itsylower end with a rotatably supported cam following roller 2tbiased into peripheral engagement with a rotatable cam 25 by means of a coil spring Eda reacting between the supporting member 3! and a washer-like disc 2% fixed to the lower end of the mandrel. The upper end of this mandrel is of conical configuration such that the diameter of those convolutions lalndisposed between the ad- Jacent groups of radially spaced convolutions as of uniform diameter, is gradually increased and decreased.

In order spirally to wrap the outer sheath 21 of materialiabout the helical convolutions 13, thereby to complete the formation of the cable, a second winding or wrapping assembly is provided which comprises a table 38 rotatably supported by means of ball bearings 40 upon afixed supporting member 39. Adjacent its peripheral edge this table fixedly carries an angularly disposed post 31 upon which is rotatably mounted a supply spool 36 for the strip material 35, conductive or insulating, from which the outer sheath 2! of the cable is formed. Movement of the conductor l2 through the mandrel 22 is effected by drawing the completed cable Ill between a pair of rollers l4 and I5, the first of which is free to rotate about its supporting axis, and second of which is adapted to be driven at a suitable speed through a driving connection H from a drive mechanism I6.

This mechanism is also utilized to drive the rotatable feed table 30 through a driving connec-- tion 34 and a gear 33 engaging the toothed periphery of the table 30; It is also utilized to drive the table 38 through a peripherally engaging gear 4| and a driving connection 42, and to rotate the cam shaft 26. In this regard it is noted that r the speeds of rotation of the rotatable elements I4, 38, 30 and are definitely inter-related within the drive mechanism l6 so that each element is operated in a predetermined timed relationship with respect to the operation of the other elements.

Preferably the filamentary element H from comprised of a fiat strip of thermo-setting or thermo-plastic material whichhas the property which the helical convolutions l3 are formed is of being settable in a fixed configuration either when heated to a predetermined temperature or when heated to a semi-plastic state and then cooled. Specifically, this element may be formed of a phenolic resin material, a methyl methacrylate resin, a vinyl chloride acetate resin, a

polystyrene resin, or a polyvinyl chloride resin material. It may be of any desired cross-sectional configuration although preferably isround or oval, in order to provide a hair line contact of the strip with the conductor I2 and thus reduce the dielectric losses and capacitance between the conductor and the outer sheath 21. For the purpose of heating this element to a temperature which will cause permanent and unstressed setting thereof in the desired helical configuration,

facilities are provided for inductively heating the mandrel 20 about which the radially spaced convolutions 13a are formed. These facilities comprise a small coil 43 disposed within the mandrel and having its terminals brought out to opposite output terminals of a high frequency current source 44 through the bore of the mandrel. This source may have an output frequency of the proper value to insure rapid and continuous heating of the external surfaces of the mandrel 20.

Briefly to consider the manner in which the above described apparatus is utilized in practicing the present improved method of making the cable shown in Fig. 2 of the drawings, it will be. understood that with the drive mechanism i8 operating, the roller (4 is driven to draw the cable [0. as completed, between this roller and the roller l5, thereby to pull the inner conductor [2 through the mandrel 20. In this regard it is noted that shortly before operation of the drive mechanism is initiated. the hi h frequency current source 44 should be activated in order that the mandrel may be inductively heated by the coil 43 to the required temperature 'forinsuring a permanent set of the filamentary element I I in the desired helical configuration. Immediately operation of the drive mechanism I6 is initiated, this mechanism, in addition to driving the roller I4, also functions to rotate the feed table 3|) about the axis of the mandrel 20, to rotate the table 38 about the same in a counterclockwise direction from the illustrated position thereof, coacts with the roller 24 gradually to move the mandrel 20 upward through the sleeve portion 300. of the feed table 30. As the mandrel is moved upward past the feed eye 301), the filamentary element ll gradually climbs up the conical end 22 of the mandrel to gradually increase the diameter of the convolution's formed by winding the element ll around the conductor l2. More specifically, the relative rotary speeds of the cam 25 and the feed table 30 are preferably such that the filament H climbs to the outer cylindrical surface of the mandrel 20 during the formation of approximately one-half. of one convolution. During continued rotation of the cam 25, the mandrel 20 is increasingly advanced through the sleeve portion 36a of the element 30 so that the filamentary element II is wound around the outer cylindrical surface of this mandrel to form spaced helical convolutions therealong. Incident to the formation of these convolutions, the material from which the element II is formed is heated above the critical temperature required for permanent setting thereof in' the desired helical configuration. When the cam 25 is advanced to bring the point 25a beneath the roller 24 and during continued rotation of, the cam, the mandrel 20 is retracted to its starting position under the influence of the biasing spring. 24a. Incident to this return movement of the mandrel to its start position, the formed convolutions l3 wound around the upper cylindrical end thereof engage the upperend of the sleeve 30a, and are pushed oif the mandrel to assume positions spaced along the conductor l2. During final movement of the mandrel back to its starting position, the element H is again wound around the conical end 22 of the mandrel tracted position, the upper end thereof is so disposed that the filamentary element II is wound directly around the inner conductor 12 of the cable to form the supporting convolutions I322. It will be apparent that by properly relating the short uniform radius portion of the cam 25 to .the variable radius portions thereof and to the speed of rotation of this cam and-the speed of rotation of the feed element 30, one or more com- 7 lating supporting structure comprises spaced groups of convolutions l3a of equal diameter which tightly embrace the conductor 12 and serve to support the radially spaced convolutions l3a from this conductor. that since the thermo-plastic or thermo-setting filamentary element II is heated to its setting or annealing temperature incident to the formation of the convolutions, a permanent set is imparted to the convolutions 13 which enhances the tendency of these convolutions to reassume the formed positions thereof when distortion pressures imposed thereon are relieved.

Concurrently with formations of the helical convolutions I3 in the manner just described, the outer sheath 2'! of insulating or conducting ma-.

terial is progressively wound around the convolutions Hi to complete the cable structure. This is accomplished through rotation of the table 38 to rotate the strip supply spool 36 around the conductor l2. Incident to such rotation the strip 35 of insulating or conducting material is withdrawn from the spool 36 and wound in edge overlapping relationship around the conductor l2 tightly to embrace the outer surfaces of the radially spaced convolutions [3a. This strip material is preferably self-adhering so that the overlapped edges thereof are bonded to prevent separation after the cable is completed. The strip 35 may be formed of tape or foil material or of a suitable braid. It may also be composed of a. wound or braided conductor consisting of conductive and insulating strands. Preferably, the table 38 is rotated in a direction opposite to the direction of rotation of the feed table 30, such that the direction of spiral of the strip 35 is opposed to the direction of spiral ofthe filamentary element ll. Opposed spiralling of the element H and the strip 35 enhances the supporting action of the convolutions i3 and thus serves to enhance the rigidity of the completed cable structure. As the completed cable is withdrawn through the rollers l4 and it may be coiled, or wound upon a suitable takeup reel for shipment.

From the foregoing explanation, it will be understood that the number of radially spaced con-- volutions I30. formed between each pair of spaced supporting convolutions l3b depends upon the relative speeds of the feed table 30 and the cam 25. By appropriately changing the relationship between these speeds within the drive mechanism l6, any desired number of convolutions l3a may be formed between ach adjacent pair of supporting convolutions l3b. It will also be apparent that the rapidity with which the diameter of the convolutions I3 is increased anddecreased between the diameter of the conductor l3 and the diameter of the mandrel depends in part upon the configuration or, length of the conical mandrel end 22, By properly relating this factor to the selected operating speed of the table 30, any desired rate of convolution diameter change can be obtained.

It should be understood that the expression "air insulated cable used throughout this specification and in the appended claims is a generic expression and refers to gaseous insulation as distinguished from solid insulating materials. It is intended that the expression include gases other than air such as the individual components of air; for example, nitrogen or other gases.

While there has been described what is at present considered to be the preferred embodiment It will also be understood of the invention, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as defined in the appended claims. I claim:

1. Apparatus for making cable having an inner conductor, comprising means for continuously moving said conductor longitudinally thereof, means operated in timed relationship with said last-named means for continuously winding a filamentary element of insulating material'around:

said conductor to form helical convolutions spaced along the length of said conductor and surrounding said conductor, and means operated in timed relationship with said last-named means for so controlling the winding of said convolutions that certain thereof are radially displaced from said conductor and the other convolutions engage said conductor at spaced points along the length thereof to support said certain convolutions from said conductor.

2. Apparatus for making ca'ble having an inner conductor, comprising a cylindrical convolution forming mandrel, means for continuously moving said conductor through said mandrel, means operated in'timed relationshipwith said lastnamed means for continuously winding a filamentary element of insulating material to form helical convolutions spaced along the length of said conductor and surrounding said conductor, and means operated in timed relationship with said last-named means for somoving saidmandrel that said convolutions are formed by alternately wrapping said strip around said mandrel and directly around said conductor, whereby the convolutions formed by wrapping said strip around said mandrel are spaced radially from said conductor and the convolutions formed by wrapping said strip directly around said conductor serve to support said radially spaced convolutions from said conductor.

3. Apparatus for making cable having an inner conductor, comprising a cylindrical convolution forming mandrel, means for continuously moving said conductor through said mandrel, feeding means operated in timed relationship with said last-named means and rotatable around the axis of said mandrel for continuously winding a fllamentary element of insulating material around said conductor to form helical convolutions spaced along the length of said conductor and surrounding said conductor, and means operated in timed relationship with said feeding means for so reciprocating said mandrel back and forth axially thereof that the predominant portion of said convolutions are formed by wrapping said.

strip around saidmandrel and the remaining portion of said convolutions are wrapped directly around said conductor, whereby the convolutions formed by wrapping said strip around said mandrel are spaced radially from said conductor and the convolutions formed by wrapping said strip directly around said conductor serve to support said radially spaced cdnvolutions from'said conductor.

r 4. Apparatus for making air insulated cable having an inner conductor, comprising a cylindrical convolution fomiing mandrel having a conical end, means for continuously moving said conductor through said mandrel, feeding means operated in timed relationship with said lastnamed means for continuously winding a filamentary element of insulating material around said conductor to form helical convolutions spaced along the length of said conductor, and means at least the conical end thereof is moved into and out of said convolutions incident to the formation thereof, thereby to so change the diameter of said convolutions that the predominant portion thereof are radially spaced from said conductor.

5. Apparatus for making cable having an inner conductor, comprising means for forming a continuous filamentary element of heat settable or heat annealable plastic insulating material into helical convolutions disposed along the length of said conductor, means for so controlling the formation of said convolutions that certain thereof are radially displaced from said conductor and the other convolutions engage said conductor at spaced points along the length of said conductor to support said certain convolutions from said conductor, and means for heating said filamentary element, thereby to cause permanent unstressed setting of said element in said convolution form.

6. Apparatus for making cable having an inner conductor, comprising a cylindrical convolution forming mandrel, means for continuously moving said conductor through said mandrel, means operated in timed relationship with said lastnamed means for continuously winding a continuous filamentary element of heat settable or heat annealable insulating material to form helical convolutions spaced along the length of said conductor and surrounding said conductor, means operated in timed relationship with said lastnamed means for so moving said mandrel that said convolutions are formed by wrapping said filamentary element alternately around said mandrel and directly around said conductor, whereby the convolutions formed by wrapping said element around said mandrel are radially spaced from said conductor and the convolutions formed by wrapping said element directly around said conductor serve to support said radially spaced convolutions from said conductor, and means for heating said mandrel, thereby to cause permanent unstressed setting of said element in said helical form.

7. The method of making cable having an inner conductor, which comprises feeding said conductor through a hollow cylindrical mandrel,

wrapping a continuous filamentary element of insulating material around said mandrel to form helical convolutions spaced radially from said conductor, withdrawing said mandrel from said convolutions to space said convolutions along the moving conductor, wrapping said element around said conductor to support said convolutions, re-

peating said wrapping steps in the order named, and heating said mandrel and thus said material, thereby to cause permanent unstressed setting of said material in said convolution form.

9. Apparatus for making coaxial cable having an inner conductor, comprising a cylindrical convolutionforming mandrel, means for continuously moving said inner conductor through said mandrel; means operated in timed relationship with said last-named means for continuously winding a filamentary element of insulating material to form helical convolutions spaced along the length of said inner conductor and surrounding said inner conductor, means operated in timed relationship with said last-named means for so moving said mandrel that said convolutions are formed by alternately wrapping said strip around said mandrel and directly around said inner conductor, whereby the convolutions formed by wrapping said strip around said mandrel are spaced radially from said inner conductor and the convolutions formed by wrapping said strip directly around said inner conductor, serve to support said radially spaced convolutions from said inner conductor, and means for wrapping conducting material on said convolutions spaced radially from said inner concertain thereof are radially displaced from said inner conductor and the other convolutions engage said inner conductor at spaced points along the length thereof to support said certain con-. volutions from said inner conductor, and means for wrapping a strip of conducting material around said certain convolutions radially displaced from said inner conductor to produce an outer conductor.

11. Apparatus for making cable having an inner conductor, comprising means for forming a continuous filamentary element of insulating material into helical convolutions disposed along the length of said conductor, means'adapted to be operated in timed relationship with said lastnamed means for so varying the diameter of said convolutions that certain thereof are radially displaced from said inner conductor and others thereof engage said inner conductor at evenly spaced points along the length of said conductor, and means for operating said two last-named means while maintaining said predetermined timed relationship between the operations thereof.

HANS D. ISENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Germany July 4, 1936 

